Magnetic material



May 15, 1928. 1,669,645

J. W. ANDREWS ET AL MAGNETIC MATERIAL Original Filed Jan. 5, 1927'men/0w:- John W And/9W5 Ram/M 6////3 Patented May 15, 1928.

1,669,645 PATENT OFFICE.

JOHN WENDELL ANDREWS, OF CHICAGO, AND RANDALL GILLIS, 0E IBERWYN, 1am-NoIs, AssIeNoRs zro WESTERN ELECTRIC COMPANY, INCORPORATED, on NEW YORK,N. 2., A CORPORATION OF NEW YORK.

MAGNETIC MATERIAL.

Application filed January 3, 1927, Serial No. 158,800. Renewed February16, 1923,

This invention relates to magnetic materials and magnet cores, and moreespecially to magnet cores for loading coils for telephone circuits andtheir method of production.

The principal object of the invention is the production of a magneticelement having low core losses and a relatively high permeability toenable a iven inductance to be obtained from a minimum amount ofmaterial, and possessing to a high degree those'electrical and magneticcharacteristics which make it highly desirable in electrical signallingapparatus, particularly in loading coils for telephone circuits.

In accordance with one embodiment, the present invention contemplatesthe construction of magnet cores of an alloy including nickel and ironin finely divided form, heat treated to have a higher inherent magneticpermeability and lower inherent hysteresis loss than iron, and combinedwith a suitable insulating material. More specifically, the inventioncontemplates the formation of the magnetcores of a nickel iron alloy infinely divided form in which the proportions of its constituents aremore than 25% of nickel and the remainder principally iron, and in aform which has proven satisfactory the nickel content beingapproximately 78 of the whole. The meta particles are treated with asolution of a nitrate which is. capable of being decomposed to form anadherent insulating coating around the particles, after which theparticles are pressed into cores of the desired shape and size. Thecores are heat treated at the optimum temperature for the particularalloy of which the cores are constructed to obtain the characteristicsdesired for the use to which the cores are to be put. 1

It is believed that the invention will be clearly understood from thefollowing detailed description of one embodiment thereofand theaccompanying drawing, in which Fig. 1 is a perspective view of a sectionof a loading coil core made in accordance with the present invention,and

Fig. 2 shows a plurality of these sections assembled to form a completedcore.

It will be understood, however, that this is merely illustrative and theinvention is not limited to the production of this form of core, but isadapted to the production of duced to a fine dust.

cores for magnetic articles of many forms.

In carrying out the present invention the magnetic material is preparedin the followmg manner. The magnetic material employed is preferablyprepared from a nickel iron alloy commonly referred to as permal- 10y,which is treated in a manner more fully described in the copendingapplication of P. Beath and H. M. E. Heinicke, Serial No. 101,179, filedApril 10, 1926, to reduce the alloy to a finely divided form. Experiencehas proven that where low eddy current losses are desired it isessential that the particles be of a small size and preferably of suchsize that all of the particles will readily pass through what isgenerally known as a one hundred and twenty mesh screen and a largepercentage pass through a two hundred mesh screen. According to oneembodiment of the invention the alloy 18 prepared by meltingapproximately 7 8 parts of nickel and 21 parts of iron in an oxidizingatmosphere and pouring the resulting alloy into a mold. When preparedaccording to the foregoing process the resulting alloy will beexceedingly brittle and is therefore particularly adapted to be reducedto a finely divided or dust form from which the finished cores aremolded.

After the brittle ingots are obtained they are passed successivelythrough progres sively reducing hot rolls which form the alloy into fiatslabs approximately thick. By the hot rolling process the size of thecrystalline structure is materially reduced, which, since thedisintegration of the material takes place mainly at the crystalboundarms, is essential in order to have a satisfactory yield of dust.The rolled slabs are broken into short pieces and are then crushed in ajaw crusher, hammer mill or any other suitable type of apparatus inwhich a further reduction occurs. The material after being passedthrough the jaw crusher is subsequently rolled in a ball mill until itis re- This dust is sieved through a one hundred and twenty mesh sieveand any residue is remelted and the foregoing operation is againrepeated to reduce the material to a finely divided form. Prior to theaddition of the insulating material the finely divided particles of thenickel iron alloy are annealed in a closed container at a temperature ofapproximately 750 C.

to 980 (3., a temperature of about 925 C. having proven to be one whichproduces very satisfactory results. It is then necessary to again reducethe annealed alloy which is now in the form of. a cake, to a finelydivided form after which itis mixed with the insulator.

According to one form of the invention, the insulator for the dustparticles is prepared by dissolving a quantity of mercuric nitrate equalto from 5 to 5.5 per cent of the finished product in a sufficientquantity of water to form a mixture which will cover the entire quantityof dust to be insulated. lhe permalloy particles are added to thesolution of mercuric nitrate and the entire mass is boiled to drynessaccompanied by constant stirring to prevent caking and to insure athorough coating ofthe individual dust particles. Shortly after the dustbecomes dry, oxides of nitrogen will be evolved which may be noted bythe appearance of brown fumes. The dust is dried for a definite lengthof time after the appearance of the fumes, which time depends upon theinsulator used, the temperature at which it is heated and thecharacteristics desired in the finished ring, a period of from fifteento thirty minutes having proved to give satisfactory results withmercuric nitrate as the insulator. The dried insulated dust parti elseare then in a form suitable for pressing into cores or rings which arepreferably formed with a pressure of approximately 200,000 pounds persquare inch. A high pressure is used in forming the rings in order toincrease their density, since it has been found that the permeability ofthe rings increases with increased density. Following this step in theprocess of constructing the cores and without unduly exposing them tothe air they are transferred to an annealing furnace in which they areannealed at the optimum annealing temperature of approximately 500 C.and cooled. A few test rings may be made of dust insulated in the abovedescribed manner and their permeability measured. Should theirpermeability be too low, it may be increased b the addition of apredetermined quantity 0% uninsulated dust to the insulated dust beforeit is pressed into rings.

A plurality of rings thus formed are then stacked coaxially to form acore on which the usual toroidal winding is applied, the number of suchrings used depending upon the existing electrical ephone circuit withwhich the loading coils are to be associated.

Although in the above described method the permalloy particles areinsulated with a solution containing mercuric nitrate amounting toapproximately 5 to 5.5 per cent of the finished product,.it is, ofcourse, to be understood that the proportions of theingrecharacteristics of the telaecaess dients may be varied withoutdeparting from the spirit and scope of the invention and that the lengthof the drying period may be varied to produce varying characteristics inthe final product. Also nitrates other than mercuric nitrate which uponheating with the permalloy decompose with the formation of an adherentinsulating material may be employed as the insulating medium, thefollowing having proved to be satisfactory substitutes: aluminum,ammonium, barium, bismuth, cadmium, chromium, c0- balt, copper, iron,lead, magnesium, manganese, mercurous, nickel, silver and zinc nitrates.Or the particles may be insulated by treating them with a nitric acidsolution which interacts with the alloy to give the nitrates of iron andnickel which in turn may be treated in the manner described above forsolutions containing added nitrates.

By using an alloy of the proportions stated in the preceding paragraphsand by following the foregoing method of insulating the individual alloyparticles and compressing the particles into cores or rings, magnetcores or rings are produced which have a high permeability. By the useof such cores or rings, inductance units having the same permeabilitywith equal or less hysteresis and eddy current losses as coresconstructed according to previously known methods, but with much lesscore volume and much less coil volume, are available.

What is claimed is:

1. As a new article of manufacture, a magnetic substance composed ofparticles of a magnetic material, and an insulating material consistingof a metal nitrate separating the particles.

2. As a new article of manufacture, a magnetic substance composed offinely divided particles of a magnetic alloy, and an insulating materialconsisting of the residue of a decomposed nitrate separating theparticles.

3. As a new article of manufacture, a magnetic substance composed ofparticles of a magnetic material, and an insulating material consistingof mercuric nitrate separating the particles.

4. As a new article of manufacture, a magnetic substance composed ofparticles of a magnetic nickel iron alloy, and an insulating materialobtained from a metal nitrate.

5. As anew article of manufacture, a magnetic substance composed offinely divided particles of a magnetic alloy composed of more than 25per cent nickel and the remainder principally iron, and an insulatingmaterial consisting of mercuric nitrate separating the particles.

6. As a new article of manufacture, a magnetic substance composed ofparticles of ill) a magnetic alloy enveloped by an insulating materialresulting from the partial decompogition 01 a nitrate.

t. The method of making magnetic structures which consists in treatingparticles of a magnetic material with a metal nitrate, and partiallydecomposing the nitrate to form a coating upon the particles.

8: The method of making magnetic structures which consists in treatingparticles of a magnetic material with a metal nitrate, and heating thetreated particles for a predetermined period of time to produce aninsulating coating thereon.

9. The method of making magnetic structures which consists in coatingthe particles of a magnetic material with a metal nitrate, and forming amass of such coated particles into a homogeneous solid.

10. The method of making n'iagnetic structures, which consists inimmersing particles of a magnetic alloy in a solution of ametal'nitrate, evaporating the solvents, and heating the resulting massto partially decompose the metal nitrate.

11. The method of making magnetic structures composed of an alloy, whichconsists in reducing the alloy to a finely divided form, heating thefinely divided mixture, again reducing the product so obtained to afinely divided form, coating the resulting product with a metal nitrate,and partially decomposing the metal nitrate upon the particles.

12. The method of making magnetic structures, which consists in reducinga magnetic alloy comprising more than per cent nickel and the remainderprincipally iron to a finely divided form, heating the finely dividedmixture at a temperature of approximately 750 C. to 980 (3., againreducing the product so obtained to a finely divided form, treatin theresulting product with a metal nitrate, i orming a mass of such treatedparticles into a homogeneous solid, and heating the solid mass at atemperature of approximately 500 C.

In witness whereof, we hereunto subscribe our names this 23rd day ofDecember A. D.,

JOHN WENDELL ANDREWS. RANDALL GILLIS.

